In recent years, magnetic recording devices, such as a magnetic disk device, a flexible disk device, and a magnetic tape device, have considerably increased in application and have increased in importance. With regards to a magnetic recording medium which is used in these devices, the recording density has been significantly improved. In particular, after the introduction of an MR head and a PRML technique, the surface recording density has further significantly increased. A GMR head, a TuMR head, and the like have also been introduced, and the surface recording density continues to increase at a pace of about 1.5 times a year.
In regard to the magnetic recording medium, there is demand for attaining a higher recording density in the future. For this reason, there is demand for attaining a high coercive force of a magnetic recording layer, a high signal to noise ratio (SNR), or high resolution. In recent years, there is continuous effect to increase the surface recording density with improvement in a linear recording density and an increase in a track density.
In the latest magnetic recording devices, the track density has reached 250 kTPI. However, if the track density increases, there is interference between adjacent tracks by magnetic recording information, and the magnetization transition region of the boundary region becomes a noise source, causing damage to the SNR. This leads to deterioration of the bit error rate, interfering with improvement in the recording density.
In order to increase the surface recording density, it is necessary to make the size of each recording bit on the magnetic recording medium finer, and to secure the largest possible saturation magnetization and magnetic film thickness in each recording bit. However, if the recording bits are made fine, the minimum magnetization volume per bit decreases, and recorded data is lost due to magnetization reversal caused by thermal fluctuation.
Since the distance between tracks is small, the magnetic recording device requires a very high-precision track servo technique, and a method in which recording is performed widely, and reproduction is performed to be narrower than recording so as to exclude the influence of adjacent tracks is generally used. In this method, while it is possible to minimize the influence between tracks, it is difficult to sufficiently obtain a reproduction output, making it difficult to secure a sufficient SNR.
As one of the methods which solves the problem of thermal fluctuation and secures the SNR and a sufficient output, there is an attempt at forming concavo-convex patterns along the tracks in the surface of the magnetic recording medium and physically separating recording tracks, thereby increasing the track density. This technique is called a discrete track method, and a magnetic recording medium manufactured by the discrete track method is called a discrete track medium.
As an example of a discrete track method, a magnetic recording medium is known in which concavo-convex patterns are formed in the surface thereof and a magnetic recording layer is formed on a nonmagnetic substrate physically separated to form magnetic recording tracks and servo signal patterns physically separated (for example, see PTL 1).
This magnetic recording medium has a ferromagnetic layer which is formed on the surface of the substrate, on which a plurality of concavo-convex patterns are formed, through a soft magnetic layer, and a protective layer which is formed on the ferromagnetic layer. In this magnetic recording medium, a magnetic recording region which is physically separated from the periphery is formed in a convex region. According to this magnetic recording medium, since it is possible to suppress the occurrence of a magnetic domain wall in the soft magnetic layer, thermal fluctuation has little effect, and there is no interference between adjacent signals. Accordingly, it is possible to form a high-density magnetic recording medium with little noise.
As the discrete track method, there are a method in which tracks are formed after a magnetic recording medium having a thin film of several layers is formed, and a method in which a thin film of a magnetic recording medium is formed after concavo-convex patterns are formed directly on the substrate surface or concavo-convex patterns are formed in a thin-film layer for track formation (for example, see PTL 2 or PTL 3).
Of these, the former method is often called a magnetic layer processing type. In this method, since physical processing is done on the surface after the medium is formed, there is a drawback in that the medium is liable to be contaminated during a manufacturing process, and the manufacturing process is unusually complicated.
The latter method is often called an embossing type. In this method, the medium is not easily contaminated during a manufacturing process. Meanwhile, since the concavo-convex shape formed on the substrate continues in the formed film, there is a problem in that the floating posture and floating height of the recording/reproducing head which performs recording/reproducing while floating on the medium become unstable.
A method is also known in which a region between magnetic tracks of the discrete track method is formed by injecting nitrogen ions or oxygen ions into a magnetic layer formed in advance or by irradiating laser (see PTL 4). Meanwhile, in PTL 4, there is no description that a resist, a mask, or the like is provided at the time of ion injection or the like. If a resist, a mask, or the like is not provided, it is difficult to control ion injection or the like only in the region between the magnetic tracks.
A technique is also known in which, when manufacturing a so-called patterned medium where a magnetic recording pattern is arranged for each bit with given regularity, the magnetic recording pattern is formed through etching using ion irradiation or through amorphization of the magnetic layer (see NPL 1 and PTL 5).
Of these, PTL 5 describes a technique in which a mask is provided in a region other than the region between the magnetic tracks on the magnetic layer, ions or the like are irradiated, and organic resist, metal, SiO2, or the like is used as a mask by ion injection.